Wind towers are fabricated by joining sections of thin-wall piping by butt welding the sections together, end to end. Generally, adjacent sections are welded around a perimeter of a joint defined between the adjoining sections to form a unitary structure. These circumferential (girth) welds and the heat affected zones (HAZs) around the girth weld create a continuous metallurgical and mechanical notch.
The girth welds of tower may be subjected to flexural stresses caused by loads within the tower or induced by the tower during turbine operation. Specifically, high winds acting on the tower may cause increased flexural stresses, and/or the weight of the turbine at the top of the tower and/or the operation of the turbine may induce high cycle vibrational flexural stresses within the tower. Over time, a combination of these factors may cause the girth welds to be subjected to high tensile stresses, which may increase the probability of cracks initiating and propagating at the welds. Weld cracking may reduce the life span of the turbine tower, which in-turn may increase costs associated with maintaining the tower.
Additionally, the continuous metallurgical and mechanical notch of the girth welds and HAZ provides a homogenous path around the full circumference of the tower through which a fatigue crack may propagate. A fatigue crack, once initiated, may progress unimpeded beyond a critical size.
Therefore, a patch, a method of preventing crack propagation in a tower, and a method of assembling a tower that do not suffer from the above drawbacks is desirable in the art.